Tuesday, October 26, 2010

Pseudomonas aeruginosa is bad news. It's the Grendel of the bacteria world - an antibiotic-resistant opportunistic pathogen that creates particular trouble for cystic fibrosis patients. Luckily for us, Beowolf has just arrived ready to dismember his foe.

Photo: A schematic representation of a bacterium 'walking' on a surface. Courtesy of Dr. Gerard Wong, UCLA.

It all started in an bioengineering lab where undergraduate students were studying videos of a bacterium called Pseudomonas aeruginosa (or P. aeruginosa for short). The students noticed something: Instead of sticking to crawling and tumbling like well-behaved bacteria, the bacteria stood up and started walking.

"Once we found that, we studied it in much more detail," said Dr. Gerard Wong, professor of bioengineering at UCLA,who pulled in post-graduate students to help with the new study.

Photo: A schematic representation of a bacterium 'crawling' on a surface. Courtesy of Dr. Gerard Wong, UCLA.

Bacteria exist in two states, Wong said. The first state is the free-swimming planktonic state in which bacteria run, crawl and tumble independently. The second state is the biofilm state in which bacteria organize together on a surface to form colonies. This colonization is the more menacing state for the medical field because bacteria that form biofilms are much more resistant to antibacterial drugs.

P. aeruginosa is a 'model' biofilm-forming bacteria because of its extreme resistance to antibiotics. Though P. aeruginosa does not cause disease on its own, it is what is called an "opportunistic pathogen." It takes advantage of those with compromised immune systems, allowing for infections to develop that would otherwise be inhibited by a healthy immune system. Cystic fibrosis patients are especially predisposed to lung infections because of P. aeruginosa invasions. Were scientists to find a way to fight biofilm formation for this and other similar types of bacteria, it could mean cures for ample types of infections.

Because of this new discovery, we may be closer than ever. The scientists have linked the walking behavior to biofilm formation. The bacteria's ability to walk, Wong said, is facilitated by special appendages called Type IV pili. What this means for us is that if the scientists can find a way to inhibit Type IV pili from developing - or chop the bacteria's legs off - they could inhibit the formation of biofilms as hosts for infections.

Any bacteria with Type IV pili could be targeted, Wong said, and the UCLA-based Wong Research group intends to do more research on the strolling pathogens.

"[This is] the tip of the iceburg," Dr. Wong said.

Below are examples of videos showing the bacteria's walking behavior:

A bacterial "launch sequence" for detaching from a surface:Bacteria attached to a surface can orient themselves perpendicular to the surface. Such 'standing' cell orientations play important roles in their life cycles. One example is how bacteria detach from a surface. Here we see that the bacterium spins on the surface, tilts upwards to a near-vertical orientation, and then launches from the surface. (FYI: Video speed is increased by a factor of 3.)

Newborn bacteria can walk before they crawl: After a bacterium divides into two daughter cells, one of the daughter cells stands up, walks away, and then detaches from the surface. This new 'walking' mechanism, where the bacterium body is upright and perpendicular to the surface, is distinct from the commonly described 'crawling' movement, where a bacterium moves while lying down with its body axis parallel to the surface.

Two daughter cells after cell division have different fates:After a bacterium divides, one of the daughter cells stands up before detaching from the surface. The other daughter cell remains behind. This difference in cell fates of two sister cells is observed in most division events.